This invention relates generally to the decoding and signal conversion of video signals. More specifically, preferred embodiments of this invention relate to an apparatus, system, and method for converting a higher definition video signal into a lower definition video signal within a Discrete Cosine Transfer (xe2x80x9cDCTxe2x80x9d) domain.
High-Definition Television (xe2x80x9cHDTVxe2x80x9d) provides an improved resolution as compared to conventional Standard Definition television (xe2x80x9cSDTVxe2x80x9d). However, HDTV is only slowly being implemented. There are a number of reasons for this slow implementation.
For example, there are several competing formats within the HDTV standard. The cost of implementing this plurality of HDTV formats is expensive. Another problem is that the HDTV signals are transmitted in a digital format. In contrast, conventional SDTV""s receive programming in an analog format that is based upon the National Television Systems Committee (NTSC) standard. Thus, because the NTSC format signals are analog and the HDTV signals are digital, they are fundamentally incompatible with each other.
Yet another problem is that the conventional SDTVs are already widely implemented. Conventional SDTVs are based upon very mature NTSC technology, and thus have achieved wide popularity, with each household in the United States averaging more than one SDTV. Also, the successive years of SDTV design and integration have reduced the cost of SDTV dramatically.
In contrast, because HDTV has just recently become available, and HDTV is a new and complex technology, HDTV can be many times more expensive than SDTVs. Because of the initial high cost of HDTV, the NTSC based SDTVs will likely continue to be popular, at least until HDTV is more available and affordable.
Until the likely transition to HDTV is complete, SDTVs will be in widespread use. However, during this transition time, more and more television transmissions will be solely in an HDTV digital format. Thus, it will be particularly useful to efficiently convert an HDTV signal to an SDTV signal.
Specifically, all of the HDTV formats support a wider screen, and up to roughly twice the resolution than the NTSC SDTV in both the horizontal and vertical directions. This increased screen format, along with the increased resolution, requires that a significantly greater amount of data be transmitted to support the HDTV formats. To transmit this additional data through the current 6 Megahertz bandwidth TV channels, the HDTV video signals are digitized and then compressed before they are transmitted. An HDTV transmission is very economical with respect to bandwidth when digitally compressed. For example, one channel of HDTV can be transmitted in the same 6 MHz bandwidth that is needed to accommodate one NTSC SDTV channel. After transmission, the HDTV video signals are then decompressed, e.g., when they reach the SDTV location, and are then converted into analog signals for display.
However, several problems arise when attempting to convert an HDTV signal for display on an SDTV. Conventional solutions utilize either a DCT domain processing or a spatial domain post-processing. The DCT-domain processing consists of two different techniques, namely a frequency cut technique and a frequency synthesis technique.
For example, the conventional spatial techniques consist of post-filtering of the decoded image. First, the signal frames are decoded. Then the decoded frames, or the fields, are filtered into a lower resolution standard definition signal. The filter selected depends upon the change in resolution desired. Conventionally, this post-filtering results in a half resolution in both the horizontal and the vertical directions of the output image. This essentially provides for a 2:1 resolution conversion.
Alternatively, in the frequency domain, a frequency cut may be utilized in the DCT domain that essentially eliminates the high frequencies. However, the results from this frequency cut are not good and thus generates a degraded signal. However, this degradation of the video signal depends upon the visual scene that is being transmitted. If there are high-frequency components that comprise at least a portion of this scene, then this frequency cut technique creates problems in the output quality display.
Specifically, in the DCT domain for the conventional frequency cut technique, only the 16 lower frequency coefficients, i.e., the coefficients in the 4xc3x974 upper left quadrant of the 8xc3x978 DCT are kept, and the rest of the coefficients are discarded. Then, a 4xc3x974 inverse discrete cosine transform (xe2x80x9cIDCTxe2x80x9d) is performed on these remaining coefficients, so as to result in a 4xc3x974 spatial block.
Another alternative in the DCT domain is the conventional frequency synthesis technique. In the frequency synthesis technique, four 8xc3x978 nearest neighbor blocks, forming a 2xc3x972 constellation, are combined to produce an 8xc3x978 block in the spatial domain.
In each of these two DCT domain frequency techniques, the resolution of the decoded image is reduced to one-half in both the horizontal and the vertical directions. Again, this essentially allows for a 2:1 conversion of the signal.
However, several problems arise from these conventional techniques. In some cases, the signal to noise ratio (xe2x80x9cSNRxe2x80x9d), and/or the subjective quality of the decoded video when displayed for the user, deteriorates to a less than desirable level.
Further, other problems include increased memory requirements and computational complexity. One problem is that in the frame field portion of the spatial domain conversion, a frame memory is required to be as large as the size of a frame of the HDTV signal. This creates a relatively high memory requirement in order to improve the video quality. If the frequency domain solution is instead utilized, then less memory is generally required because the conversion is conventionally done in the DCT domain. This frequency domain lower memory requirement is because the frame memory is essentially the same size as the frames associated with the output signal, i.e., the lower resolution signal. However, the problems with the output quality become more pronounced. Thus each solution has its respective tradeoffs.
What is needed is a device and method for converting a higher resolution signal to a lower resolution signal while reducing at least one of the memory size requirement and the computational complexity requirement, yet maintaining a relatively high-quality signal for output on a display.
Embodiments of the present invention are best understood by examining the detailed description and the appended claims with reference to the drawings. However, a brief summary of embodiments of the present invention follows.
Briefly described, an embodiment of the present invention comprises a device and a method that provides for the improvement of the conversion of a higher definition signal into a lower definition signal.
Embodiments of the present invention comprise a new device and technique to realize an improved conversion of a higher definition signal into a lower definition signal, while reducing the relative memory requirement and/or the relative computational complexity requirement, yet maintaining a relatively good quality of the output video signal. This improvement is achieved by utilizing a diagonal matrix in place of at least one identity matrix while processing the signal in the DCT domain.
For example, in one embodiment of the present invention, a Motion Picture Experts Group 2 (xe2x80x9cMPEG-2xe2x80x9d) digital signal may be received and decoded and/or decompressed. Next, the signal is placed in the DCT domain. In this embodiment, the signal is preferably in a two-dimensional domain and in a matrix form. The signal is then processed.
During processing, the signal is first pre-multiplied with a predetermined diagonal matrix, that may be referred to as a xe2x80x9cBxe2x80x9d matrix. Then, the results are post-multiplied again with the same diagonal, or B, matrix. After the pre-and post-multiplying of the signal, the resulting smaller-size DCT matrix is then inverse DCT transformed over the smaller size. Finally, the signal is then made available for output, e.g., to a display such as a television or a computer monitor.
In one embodiment, the present invention is utilized to convert an HDTV signal into an SDTV signal, preferably providing a 2:1 conversion. However, in other embodiments of the present invention, techniques may be utilized to provide any N-to-M conversion ratio, where M is a non-zero integer and where N is a non-zero integer that is greater than M.
In other alternate embodiments, techniques of the present invention may be utilized to convert any relatively higher resolution signal to a relatively lower resolution signal. For example, while some embodiments receive an MPEG-2 type signal, other embodiments of the present invention are also applicable to any signal, including a non-compressed and non-encoded signal. Any signal that may be processed, for example, in a digital signal processor (xe2x80x9cDSPxe2x80x9d), may be converted to a lower resolution utilizing the present invention.
In yet other alternate embodiments of the present invention, any signal, not merely a television signal, may be converted from a higher resolution or complexity signal to a lower resolution or complexity signal by utilizing the present invention.
In other alternate embodiments, the present invention may be utilized as a portion of an algorithm to convert signals to a lower resolution or a lower complexity. Also, embodiments of the present invention may be utilized with a DSP, or may be implemented either partially or wholly in electrical circuitry.
Other arrangements and modifications will be understood by examining the detailed description and the appended claims with reference to the drawings.